Grab yourself an emulation of the excellent Oberheim OBX OBXa and OB8 synthesizers for free from developer 2DaT.

Now available as an audio unit compatible with Logic Pro and Logic Pro X, here's what 2DaT has to say:

"Obxd is emulation of famous ob-x, ob-xa and ob8 synths.

While not copying originals , some of the features were taken to a better point. Continuous blendable multimode filter (hp-notch(bp)-hp in 12 db mode and 4-1 pole in 24 db mode). VAM button is last played note allocation mode. 32 and 64 bit versions included."